1. Field of the Invention
This invention relates to a control apparatus for a tandem type of a hot rolling mill including a plurality of rolling stands, which controls a width of a rolled material by controlling an interstand tension of the rolled material positioned between adjacent rolling stands.
2. Description of the Background
As for finishing hot rolling mills, to obtain a desired thickness and width of a rolled material, a control apparatus for the finishing hot rolling mill is initialized by calculating a roll gap between rolls of a rolling stand and a rolling speed in accordance with rolling conditions and the properties of the rolled material.
FIGS. 1 and 2 show one example of a conventional control apparatus for a finishing hot rolling mill. FIGS. 1 and 2 share a drawing of the control apparatus and show it in cooperation.
A finishing hot rolling mill is shown in FIGS. 1 and 2, which usually includes four through seven rolling stands disposed in tandem.
FIGS. 1 and 2 also show a rolled material 1, rolling stands 2(2a.about.2e), load detectors 3(3a.about.3e) such as load cell, rolling motors 4(4a.about.4e) for driving rolls, speed controllers 5(5a.about.5e), loopers 6(6a.about.6d) controlling an interstand tension of the rolled material 1 positioned between adjacent rolling stands 2, tension detectors 7(7a.about.7d) attached to the loopers 6, and roll gap controllers 8(8a.about.8e).
A delivery side width gauge 9 is disposed at the delivery side of a roughing rolling mill positioned at the entry side of the finishing hot rolling mill. An entry side pyrometer 10 measures a temperature of the rolled material 1 which is needed for calculating the initial value for the finishing hot rolling mill. Further, a delivery side width gauge 11, a delivery side pyrometer 12 and a delivery side thickness gauge 20 are disposed at the delivery side of the finishing hot rolling mill in order to check the qualities of the product.
In rare cases, a thickness gauge and a width gauge are respectively disposed between the rolling stands 2, thereby measuring the thickness and width of the rolled material 1 on all the way of the rolling process and using them for setting or controlling. Such system is rarely adopted and it makes a difference in a control system whether the thickness gauge and the width gauge are respectively disposed between the rolling stands 2 or not. The following is the conventional control apparatus as shown in FIGS. 1 and 2, which can be easily modified, even if the thickness gauge and the width gauge are disposed between the rolling stands 2.
In FIGS. 1 and 2, a setter 19 calculates a roll gap and a rolling speed of each roll of the rolling stands 2 in accordance with rolling conditions and target values of a thickness and a width of the rolled material 1, and sets the roll gap and the rolling speed to a subordinate controller, that is, the roll gap controllers 8 and the speed controllers 5.
Looper tension controllers 14(14a.about.14d) input each looper angle formed by a looper arm supporting each of the loopers 6 and a horizontal line, and each interstand tension detected by each of the tension detectors 7, thereby calculating and outputting correcting speeds for the rolling motors 4, which are used for obtaining target tension values and target looper angle values.
Power source for revolving the loopers 6 may be looper electric motors, looper hydraulic cylinders or looper hydraulic motors, but whether which power source is adopted is not cared at this point. Command values of the power sources may be command values of torque(current) or speed in case electric motors are adopted as the power sources. Command values for the power sources may be command values of torque or pressure in case hydraulic power is adopted as the power sources. In FIGS. 1 and 2, drawings of the power sources are omitted.
A roll gap thickness controller 16 respectively outputs roll gap command values to the roll gap controllers 8 by feeding back a detected thickness value measured by a delivery side thickness gauge 20 so that a thickness of the rolled material 1 accords with the target value thereof. In some cases, a thickness control is executed by using a gauge meter thickness calculated on the basis of gauge meter equation, that is, the gauge meter thickness is calculated on the basis of roll forces detected by load detectors 3 and roll gap command values.
The gauge meter equation is represented as follows: EQU h=S+P/M
h is a delivery side thickness of a rolled material. S is a roll gap command value. P is a roll force. M is a mill modulus.
The above is a basic control system for the finishing hot rolling mill, but a width control for a rolled material is sometimes added to the above described system.
Each target value of interstand tensions is calculated on the basis of a difference between a width value detected by the delivery side width gauge 11 and a target width value thereof, and is then sent to each of the looper tension controllers 14. This control method is so-called an FB (Feed Back) control.
Further, an FF (Feed Forward) control may be used for reducing a width of the rolled material 1 by means of tracking a width detected by the delivery side width gauge 9 with the progress of the rolled material 1 and providing a large tension at the wide width portion of the rolled material 1 during the rolling process.
As for a usual width behavior of the rolled material 1, as an interstand tension becomes larger, a width of the rolled material 1 reduces. Further, as a temperature of the rolled material 1 becomes higher, an effect on a width variation of the rolled material 1 becomes larger. Consequently, either an FB control or an FF control takes account of a relation with the width variation, an interstand tension and a temperature.
Either the FB control or the FF control is integrated into a conventional tension thickness controller 21 shown in FIG. 2. A roll gap variation of the rolling stand 2, which is regarded as a disturbance against a width control other than a width variation produced at a roughing rolling mill, may take an effect on a width change of the rolled material 1. In case a roll gap is reduced by the rolling stand 2, a width of the rolled material 1 spreads. On the contrary, in case a roll gap is opened by the rolling stand 2, a width of the rolled material 1 becomes narrow. Generally speaking, a final width of a delivery side width of the rolled material 1 is determined by combining a width spreading effect at the point just below the rolling stand 2 with a width narrowing effect at the middle of the adjacent rolling stands 2.
The most upstream stand 2a has a large effect on spreading a width of the rolled material 1, since a reduction at the rolling stand 2a is usually big. Accordingly, if the rolling stand 2a changes a roll gap by use of the AGC (Automatic Gauge Control), the width variation becomes larger.
As described above, in case an interstand tension is changed to control a width of the rolled material 1, this change results in not only a variation of the width but also a variation of the thickness thereof. That is, if the interstand tension increases, the thickness thins. If the interstand tension decreases, the thickness becomes thick. Especially, if an interstand tension is changed at the most downstream stand 2e, this change has a big effect on a thickness of the rolled material 1.
Accordingly, it is impractical to correct a width in a large quantity by changing an interstand tension. An ability of a width control is limited at the most downstream stand 2e. In practical, such tension width control is applied to the rolling stands 2 disposed at the upstream side.
However, there is a problem in the present tension width control.
For example, if an interstand tension is increased to narrow a width of the rolled material 1, a roll force and a mill stretch decrease. As a result of which, a thickness of the rolled material 1 becomes thin, a roll gap of the rolling stand 2 becomes small by the AGC, and a width of the rolled material 1 is widen at the point just below the rolling stand 2. Consequently, a width narrowing effect controlled by a tension change is almost canceled in part by a width spreading effect due to a decrease in a roll gap. Therefore, to control a width of the rolled material 1 so as to accord with a target width, much more tension is required.
Further, in general, a response of a tension change by means of a looper control takes 1 second to reach a 95 percent of the reference value. Since it usually takes about three times as much as the time until a width control is finished, a quicker response is desired.